Rechargeable batteries are used in a wide range of applications demanding high specific energy, high rate capabilities, long cycle life and long calendar life. The quality of the active materials constituting the electrodes of the batteries is paramount in order to reach these targets. The design and quality of the electrodes constituted of these materials are critical as well. For example, higher cathode thickness is detrimental for high rate performances but favourable for higher energy content. Another example is the porosity of electrodes for lithium-ion batteries because the porosity controls the amount of electrolyte which can be soaked and spread within the electrode when liquid electrolyte is used to provide the ionic conduction between the electrodes. In liquid electrolyte batteries, electrodes have porosities in the range of 30% to 50% in order to accommodate sufficient electrolyte penetration. Porosity can be achieved in many different ways such as thickness reduction of the electrode by mechanical means, electrode making process, electrode formulation and in certain cases by the adjunction of pore forming additives. Active materials themselves impact porosity. In order to insure reproducible electrodes characteristics, battery manufacturers put a lot of emphasis on the supply of reproducible raw materials and on in-house statistical process controls (SPC).
In the case of solid polymer electrolyte lithium batteries, the polymer itself is the ionic conductive media. Therefore, there is no need to impregnate the electrode with liquid and the electrodes need not have any porosity for the purpose of ionic conduction. The solid polymer plays the role of both a binder and electrolyte.
The optimal configuration of an electrode for solid polymer electrolyte lithium batteries can be described as the highest active material loading within the polymer matrix which can be achieved by optimal spatial arrangement of the electrode material particles. As the ratio of active material to binder increases, there is more chance of trapping air or gas in the spacing between the contacting electrode material particles. This trapped air or gas is responsible for the measured porosity of the electrode.
The spatial arrangement of the electrode material particles within the electrode is greatly influenced by their intrinsic and mutual properties i.e. particle shape, interparticle interactions and particle size distribution. Related parameters such as the effectiveness of the polymer binder to wet the electrode material particles can also influence the spatial arrangement of the particles within the electrode.
Therefore, there is a need for an electrode for solid polymer electrolyte batteries with improved active material loading and improved spatial arrangement of the material particles within the electrode and for electrode materials which contribute to increasing the loading of an electrode manufactured therewith.